Insecticidal sheets, insecticidal filaments, etc. made of thermoplastic resins, for example, olefin-based resins such as polyethylene into which insecticidal compounds are kneaded are well known, as well as the manufacturing processes therefor: that is, an insecticidal sheet is manufactured by melting and kneading a thermoplastic resin composition comprising an insecticidal compound such as an insecticide, and molding the knead mixture into a sheet or a desired shape by an ordinary molding method; and insecticidal filaments are manufactured by the melt spinning method.
It is known that such an insecticidal compound-containing thermoplastic resin is manufactured by mixing one kind of a thermoplastic resin or a thermoplastic resin mixture of two kinds of thermoplastic resins which have different solubilities to an insecticidal compound, with the insecticidal compound, and melt-kneading the resulting mixture (e.g. JP-A-4-65509 and JP-A-8-302080).
This insecticidal resin composition may be directly used as a raw material for sheets or filaments, however, in many cases, is used in the form of pellets as the thermoplastic resin composition for a master batch containing an insecticide at a high concentration, and usually, such pellets are mixed with a newly added thermoplastic resin in order to adjust the concentration of the mixture to a desired value, before the manufacturing of sheets or filaments.
In this case, the thermoplastic resin composition for the master batch and the sheets or the filaments are manufactured at different sites. Therefore, it is needed to transport the previously manufactured insecticidal compound-containing thermoplastic resin pellets for the master batch to the manufacturing site for the sheets or the filaments, and it is also needed to store such pellets over a long period of time until the distribution thereof.
However, the transportation and the storage of such pellets containing an insecticide at a high concentration have some problems. That is, because the pellets are often exposed to a high temperature atmosphere depending on the weather or the sites, transported or stored over a long period of time, the contained insecticidal compound bleeds out to the surfaces of the pellets to make the pellets sticky. Thus, the blending or the automatic blending of such pellets became markedly hard, and the insecticidal compound in the pellets evaporate, as the case may be.